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AIP conference proceedings

Microwave parametric amplifiers using externally pumped Josephson junctions

O. H. Soerensen, J. Mygind, N. F. Pedersen

Published Jan 1, 1978• 6 citations
Publisher

Abstract

Externally pumped parametric amplifiers are discussed. Theory and experiments on the singly degenerate parametric amplifier based on a Josephson junction are presented. Advantages and limitations of the singly degenerate and doubly degenerate parametric amplifiers are discussed. Some plans and proposals for future research are presented.
DOI
10.1063/1.31347

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IEEE Transactions on Magnetics•Jan 1, 1977•16 citations
A unified theory of the singly and doubly degenerate Josephson-junction parametric amplifier is presented. Experiments with single junctions on both amplifier modes at frequencies 10, 35, and 70 GHz are discussed. Low-noise temperature (∼100 K, single sideband (SSB)) and reasonable gain (∼8 dB) were obtained at 35 GHz in the singly degenerate mode. On the basis of the theory and experiments, a general procedure for optimizing junction parameters is discussed and illustrated by the specific design of a 100-GHz amplifier.
The signal and noise properties of two basic types of externally pumped parametric amplifiers, using Josephson junctions with low capacitance, are calculated. The first type is a single- frequency nondegenerate amplifier and second one is a two-frequency degenerate amplifier, referred to sometimes as SUPARAMP. Calculations are based on the conventional RSJ model of the Josephson junction. In contrast to the works published earlier, the most realistic open circuit approximation is used for idler combinational frequencies, as well as for the pumping frequency harmonics. A single-frequency amplifier is shown to have relatively low noise temperatures (T_{N} \approx 25T) at signal frequencies of the order of the Josephson junction characteristic frequency ωc. On the other hand, SUPARAMP can have much lower noise but at lower frequencies, and it behaves approximately as a usual parametric amplifier with a critical frequency\omega_{cr} \approx 0.2 \omega_{c}.
Josephson junctions are quantum mechanical devices with sinusoidal nonlinearity and their use as amplifiers of non-classical microwaves in cavities at low temperatures, is discussed. Self-pumped amplifiers as well as externally pumped three- and four-photon amplifiers are considered, and a quantum theory that describes their operation is developed. It is shown that the sinusoidal nonlinearity can be expanded into a series of terms, the first few of which are familiar from quantum optical amplifiers that use nonlinear optical materials, while the others are higher order corrections.
We present the results of an experimental effort to generate squeezed microwave radiation using the phase-sensitive gain of a Josephson parametric amplifier. To facilitate the interpretation of the experimental results, we first present a discussion of the theory of microwave squeezing via Josephson parametric amplifiers. This is followed by a detailed description of the device fabricated for our experiment. Experimental results are then presented for the device used in both the doubly degenerate or four-photon mode and for the degenerate or three-photon mode. We have observed parametric deamplification of signals by more than 8 dB. We have demonstrated squeezing of 4.2-K thermal noise. When operated at 0.1 K, the amplifier exhibits an excess noise of 0.28 K when referred to the input. This is smaller than the vacuum fluctuation noise level \ensuremath{\Elzxh}\ensuremath{\omega}/2k=0.47 K. The amplifier is thus quieter than a linear phase-insensitive amplifier in principle can be.
Gain and noise properties of a non-degenerate one-frequency parametric amplifier using a self-pumped Josephson junction are investigated both theoretically and experimentally. The amplifier uses the phenomenon of microwave negative resistance of the junction. Theoretical analysis made in usual resistively shunted junction (RSJ) model shows that the minimum noise temperature is equal to approximately 42T. It takes place at a signal frequency f close to the junction characteristic frequency f0. Maximum effectivity (the product of the square root of power gain and relative bandwidth) can reach 0.4 at f≃f0. Gain up to 20 dB was obtained at X-band using amplifier with Nb-Ta point-contact junction. Minimum noise temperature at T = 4.2K was about 200K.